The present invention relates to printing apparatus, in particular to clearance of jammed sheets as could be found in the post-fuser path of a xerographic printer or copier.
In electrophotographic printers commonly in use today, a charge-retentive member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the charge-retentive surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the original document. Subsequently, the electrostatic latent image on the charge-retentive surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the charge-retentive member to form a powder image on a photoconductive area. This image is subsequently transferred to a support surface, such as copy paper, to which it is permanently affixed by heating or by the application of pressure. Following transfer of the toner image to a support surface, the charge-retentive member is cleaned of any residual toner that may remain thereon in preparation for the next imaging cycle.
One approach to fixing, or xe2x80x9cfusing,xe2x80x9d the toner image is applying heat and pressure by passing the copy paper or print sheet containing the unfused toner images between a pair of opposed roller members at least one of which is internally heated. During this procedure, the temperature of the toner material is elevated to a temperature at which the toner material coalesces and becomes tacky. This heating causes the toner to flow to some extent into the fibers or pores of the sheet. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to become bonded to the sheet.
After the fusing step, it is common that the resulting output sheet be fed to a subsequent processing station, such as an inverter, collator, stapler, booklet maker and the like. In order to direct a sheet emerging from the fuser rolls to the next processing station, it is common that the volume of space immediately downstream of the fuser in the process direction, which can be called the xe2x80x9cpost-fuser pathxe2x80x9d be effectively shaped in a funnel configuration, so that a sheet passing through the post-fuser path is directed toward a fairly narrow opening, such as toward a stapler.
FIG. 1 is an elevational view of some basic elements of an electrostatographic printer, illustrating a practical problem addressed by the present invention. Blank sheets are drawn one at a time from a supply stack 100 and conveyed, by known means, through a paper path 102 along a process direction P. At a charge-retentive surface such as on photoreceptor 104, marking material forming an image is electrostatically transferred to each sheet by one or more corotrons 106 or equivalent devices. Following transfer, the sheet is sent through fuser rolls 108 and 110. After fusing, the sheet can be sent on for further processing, such as stapling or binding.
Following the fuser along process direction P, it is typical that the sheets pass through the post-fuser path which is of a general funnel shape, such as formed by surfaces of baffles 10 and 12, whereby the vertical width of the path decreases to a relatively narrow slot 14, through which the sheet can be directed to a subsequent processing station.
As can be seen in FIG. 1, a problem can occur if the subsequent processing station following slot 14 is unable to accept input of a sheet, such as if the station is malfunctioning. If a sheet S cannot be accepted through slot 14 and is nonetheless pushed forward by the motion of fuser rolls 108, 110, the sheet S will jam and be compacted between surfaces formed by baffles 10 and 12. The funnel-like surfaces of the baffles 10, 12 tend to exacerbate a jamming problem, because the shape causes a very compact accordion-folding of the moving sheet. The post-fuser path will fill up quickly with one or more sheets, and the compaction of sheets is liable to damage the hardware around baffles 10 and 12.
The present invention is directed toward avoiding and obviating damage that can be caused in a post-fuser path in a printing apparatus, or indeed any post-roller path in any apparatus which feeds sheet material.
U.S. Pat. No. 5,245,395 discloses a fusing apparatus wherein a baffle associated with stripper fingers on an exit side of the apparatus imparts an arcuate profile on sheets emerging from the apparatus; this tends to prevent longitudinal waves from forming in the sheet.
U.S. Pat. No. 5,822,668 discloses a fusing apparatus which pivots open on its exit side for jam clearance. Various stripper fingers and plates are mounted on the pivoting exit side of the apparatus.
According to one aspect of the present invention, there is provided an apparatus useful in moving sheets, comprising a first roller and a second roller, forming a nip therebetween; means defining a substantially enclosed post-roller path downstream of the nip along a process direction toward an output opening; and opening means for increasing a size of the post-roller path.